Incinerator toilets apply heat to human waste, thereby evaporating urine, and dehydrating and oxidizing (burning) the dried residue to an ash which is accumulated in an ash pan and on occasions removed for disposal elsewhere. A removable ash pan is desirable for convenience. Such an ash pan must be sturdily constructed to withstand the rigors of handling, banging, and emptying and be of a material to provide such construction. If the ash pan also forms an integral part of the incinerator chamber, i.e., containing the deposited waste during actual incineration, it is also subjected to intense heat and may be deformed and chemically attacked.
If the ash pan is located beneath the source of heat as in the case of a radiant electric heater being supported above the waste, heat is transferred into the waste by direct radiation and by conduction of heat through the material composing the ash pan. If conductance of the material is low, then efficiency of the heat transfer process is greatly impaired, thereby extending the time of incineration which, in turn, limits the rate of usage of the toilet as well as increasing the amount of energy used as well as the cost of operation.
Regarding human waste as a mix of liquid waste and solid waste, considerable improvement in the rate of incineration can be had by separating the liquid from the solid and applying heat to both phases simultaneously; otherwise, the liquid waste must first be evaporated, then the solid waste dehydrated, then elevated in temperature to the point of ignition. Obviously, if all three actions can proceed simultaneously, substantial savings in time and energy can be realized.
Stainless steel offers toughness in handling and is sufficiently heat and chemically resistant; however, it exhibits poor heat conductivity, on the order of 0.07 cal/deg C/sq cm/cm. Therefore, if the ash pan is of stainless steel and constructed for example as shown in U.S. Pat. No. 3,890,654, with both the inner and outer pans being of stainless steel, the raised center portion will actually inhibit the evaporation process because it shadows the bottom of the ash pan from the heater and, yet, does not conduct the heat gathered at its top portion. The resulting efficiency is greatly reduced. An ash pan similar to that shown in U.S. Pat. No. 3,890,654, with both the inner and outer pans formed of stainless steel and welded together with a dead space therebetween, has been used in the past.
Aluminum is ideal from standpoint of heat conductivity, being some 10 times more conductive than stainless steel. It is also relatively inexpensive and readily available. Aluminum of the grade for forming is not resistant to rough handling and easily deforms. It also has a low softening-point temperature.